text: It has been shown that, due to the nocebo effect, warning patients about side effects of drugs can contribute to the causation of such effects, whether the drug is real or not. This effect has been observed in clinical trials: according to a 2013 review, the dropout rate among placebo-treated patients in a meta-analysis of 41 clinical trials of Parkinson's disease treatments was 8.8%. A 2013 review found that nearly 1 out of 20 patients receiving a placebo in clinical trials for depression dropped out due to adverse events, which were believed to have been caused by the nocebo effect.
  In January 2022, a systematic review and meta-analysis concluded that nocebo responses accounted for 72% of adverse effects after the first COVID-19 vaccine dose and 52% after the second dose.
  Many studies show that the formation of nocebo responses are influenced by inappropriate health education, media work, and other discourse makers who induce health anxiety and negative expectations.